In these studies we shall attempt to define the immunologic and immunogenetic basis of mammary tumor development. We shall continue to study the role of T and B cells and thymic stroma in the control of these tumors. In addition our studies will be redirected (in collaboration with Dr. R. Michael Williams) towards the identification of genes in the H-2 region which may confer resistance to development of mammary tumors. These studies will be done in both thymectomized and unoperated animals using thymus in millipore chambers, thymus grafts and reconstitution of thymectomized mice with lymphocytes (Ly 1 plus or Ly minus 2, minus 3 positive). Also, we will investigate the role of suppressor cells by eliminating these cells by treating the lymphocyte suspension with IJ region antibodies in thymectomized mice. Mapping of H-2 resistance will be done by using congenic strains of mice. These congenic strains are of such H-2 composition that we will test the importance of I-J region differences in the genetic control of tumor resistance. In another group of related experments, we will also study in collaboration with Dr. Harvey Cantor the immune functions of thymectomized mice reconstituted with thymus in millipore chambers to identify possible reconstitution to some subsets of lymphocytes and not all. All our studies will be significant from the point of view of general and basic immunobiology and also from the point of view of tumor immunology and immunogenetics.